In recent years, techniques have been sought that can efficiently produce monocyclic aromatic hydrocarbons having 6 to 8 carbon atoms (such as benzene, toluene, ethylbenzene and xylene, hereinafter, which are collectively referred to as a “BTX fraction” or “BTX”), which can be used as high-octane gasoline base stocks or petrochemical feedstocks and offer high added value, from feedstocks containing a polycyclic aromatic fraction such as a light cycle oil (hereinafter, also referred to as “LCO”), which is a cracked light oil produced by a fluid catalytic cracking (hereinafter, also referred to as “FCC”) apparatus, and has been mainly used as light oil or heavy oil fraction.
Examples of known methods for producing a BTX fraction from a polycyclic aromatic fraction include the following methods.
(1) Methods of hydrocracking hydrocarbons containing a polycyclic aromatic fraction in a single stage (see Patent Literatures 1 and 2).
(2) Methods of subjecting hydrocarbons containing a polycyclic aromatic fraction to a hydrotreatment in a preliminary stage and then hydrocracking in a subsequent stage (see Patent Literatures 3 to 5).
(3) A method of converting hydrocarbons containing a polycyclic aromatic fraction directly into a BTX fraction using a zeolite catalyst (see Patent Literature 6).
(4) Methods of converting a mixture of hydrocarbons containing a polycyclic aromatic fraction and light hydrocarbons having 2 to 8 carbon atoms into a BTX fraction using a zeolite catalyst (see Patent Literatures 7 and 8).
However, the methods of (1) and (2) require the addition of high-pressure molecular hydrogen, and there is a problem of a high level of hydrogen consumption. Further, under the hydrogenation conditions, an unnecessary LPG fraction is by-produced in a large amount during production of the target BTX fraction, and not only is energy required to separate the LPG fraction, but also the feedstock efficiency deteriorates.
The method of (3) is not sufficient in terms of conversion of the polycyclic aromatic fraction.
The methods of (4) is designed to improve the thermal balance by combining a production technique for BTX which uses light hydrocarbons as a feedstock and a production technique for BTX which uses hydrocarbons containing a polycyclic aromatic fraction as a feedstock, but is not designed to improve the yield of BTX from the polycyclic aromatic fraction.